Airplanes flying through super-cooled clouds around airports can cause condensation that actually results in more snow and rain for nearby areas, according to a new study. The perfect conditions for such a freaky weather event occur about 5% of the time—but 10% to 15% in winter—according to the study’s lead author. Aircraft take off into the wind, so if they are generating extra ice particles upwind of an airport, the result can be snow right on the airport. That could mean planes will require more de-icing.

The team was investigating holes or canals that are sometimes seen drilled in clouds after an airplane has passed through. They found that increased snow and rainfall occurs in areas where the unusual cloud holes appear, usually within 60 miles of the airport. The added rain or snowfall occurred when the clouds were made up of water droplets that were colder than freezing, but which had not yet frozen: When an airplane passes through one of these clouds the movement causes a sudden cooling of the air, sometimes down to the critical point where the droplets freeze. They then can fall to earth as snow or rain.